Method for producing furfural and charcoal



United States Patent METHOD FOR PRODUCING FURFURAL AND CHARCOAL Eduard Farber, Washington, D. C., assignor, by mesne assignments, to Cumberland Corporation, Lexington, Ky., a corporation of Kentucky No Drawing. Application July so, 1954, Serial No. 446,940

5 Claims. (Cl. 202--3) dust, slivers, or shavings to produce improved yields.

of high quality charcoal.

'Wood distillation is an ancient art. Methyl alcohol, acetic acid and similar materials have historically been produced by the distillation of wood. Similarly, it is old in the art to produce turpentine and the like from the distillation of certain soft woods. It is known to produce charcoal by heating wood above the exothermic decomposition temperature. None of the practices of the prior art, however, are designed to produce consistently high yields of furfural in good concentration and to yield a residual charcoal product of high quality. The conditions which have been observed for the production of organic acids and turpentine from wood are'inappropriate to produce high yields of furfural, which is formed by the conversion of the pentosans which are present in wood. Indeed, some of the organic acids obtained by prior processes may be considered to be degradation products of furfural. The conditions which are requisite to the optimum yield of furfural from Wood are such as to suggest that the wood from which the furfural is to be produced should be present in relatively small particle sizes characterized by a large surface area. Sawdust is a typical example of such finely divided wood. However, as is well known in the art, high quality commercially useful charcoal cannot feasibly be produced from sawdust.

It is accordingly a primary object of this invention to provide a method for producing by heat treatment of wood consistently high yields of furfural and a residual charcoal product of quality.

It is another object of the invention to provide a method whereby furfnral'rnay be derived from relatively large wood pieces, such as wood chips, without substantial degradationinto low molecular weight organic acids and high molecular weight tars. It is another object of the invention to provide a method for producing furfural and charcoal from wood by using mixtures of wood of different particle size, the difference in heat transfer between the various particles in the mixture being availed of to provide .zones of different temperatures, such that a predominant part of the mixture, i. e., the large pieces of wood, is maintained at a temperature optimum for the production of furfural, while another portion of the mixture, i. e., the small pieces of wood which are in close contact with the large pieces, reach a sufficiently high temperature to exothermically decompose and give olf substances which favor the production of furf ural from the large pieces.

It is an additional object of the invention to provide a method for producing from wood a crude distillate char- "ice fural than that which is obtained from conventional prior wood distillation methods.

provisionof a method whereby the production of furfural from the pentosans present in relatively large pieces of wood is catalyzed by organic acids generated in situ by the exothermic decomposition of wood particles substantially smaller and having a substantially greater-surface area than the large wood pieces from which the furfural is primarily derived.

It'is still a further object of the invention to produce optimum yields of furfural from relatively large wood pieces at temperatures below the exothermic decomposition temperature of the wood chips and normally at temperatures not in excess of about 275 C.

It is an additional objectof the invention to provide a process wherein relatively large wood pieces are heated to a temperature requisite for the conversion of pentosans to vvfurfural by the exothermic decomposition of small particlcs'ofwood having a large surface area such as sawdust.-

It is another object of the invention to. provide a method whereby the crude distillate obtained by the heat treatment of wood is not contaminated by the addition of materials foreign to the wood during the distillation step.

It is an additional object of the invention to provide a method for the recovery of furfural from Wood which leaves a wood residue after the furfural forming step. which is in perfect form for conversion to charcoal.

In accordance with this invention, there is provided a mixture of relatively large wood pieces, such as chips andsawdust, having a particle size of not larger than 6 mesh, there being present in said mixture from about one to about ten parts by weight on a dry basis of said sawdust for each ten parts by weight of said chips. The mixture so provided is heated gradually to an elevated temperature I sufficiently high to effect exothermic decomposition of said chips to furfural.

- relatively large wood pieces and sawdust particleshaving acterized by a substantially higher concentration of fur a large surface area, andwhich are capable of-reaching the temperature of exothermic decomposition substantially before appreciable exothermic decomposition of the large wood pieces occurs, it is possible to obtain cone sistently high yields of furfural from the chips at tempera tures below the exothermic decomposition temperature of the chips,and to convert the chips into awood residue suitable for the production of high quality charcoal.

The large wood pieces or chips, which are employed in the mixture which characterizes this invention, may have a minimum dimension, i. e., length, Width, or thickness of at least'one-eighth'of an inch. However, the chips can have a substantially larger minimum dimension, for example, from about three-eighths of an inch to about 'fiveeighths of an inch, for the more porous woods, such as poplar and birch. The wood chips may be on the order of one to four or more inches in maximum dimension. Chips, such as are produced by conventional wood chipping apparatus, are suitable.

It is a function of the sawdust,-which is characterized by a large surface area, to decompose exothermically and thereby produce in situ organic acids, more specifically, formic, acetic, and some propionic acid, which acids are effective to catalyze the conversion of the pentosans present in the chips to furfural at a temperature substantially below that at which the chips undergo appreciable exothermic decomposition. The sawdust is of such a form as to be more rapidly heated throughout than the large wood chips. I I a mesh size between about and'20. The small wood particles serve also to furnish by exothermic decomposition part of the heat necessary for heating the large wood chips.

It is important that the mixture contain from about oneto about ten parts by Weight on a dry basis of the small wood particles having a large surface area for each ten parts by weight of the relatively large wood chips. Particles of wood of intermediate size, i. 'e., larger or different from the sawdust but smaller than the large wood chips, can be present in the reaction mixture, and the invention embraces mixtures containing wood particles of such intermediate size. The optimum ratio of'sawdust to the large wood pieces will vary somewhat, depending upon the moisture content of the wood employed.

When-wood having a moisture content of from about 10% to about by weight is employed, it is preferred that the reaction mixture contain from about one to about five parts by weight of the sawdust'for each'ten parts by weight of the wood chips. In all cases, it is necessary that there be sufficient quantity of sawdust present in the mixture to produce a sufficient quantity of organic acids to catalyze the conversion of the pentosans in the wood chi s to fur fural.

On the other hand, if quantities of sawdust substantially in excess of the above specified are employed, the reaction mixture may become too compact with the result that the volatile materials may not develop freely and thereby reduce the yield of furfural.

"In the practice of the invention, the wood mixture, as above described, is heated to a temperature requisite to sheet exothermic decomposition of the sawdust, but not sufficiently high to occasion appreciable exothermic decomposition of the wood chips. The wood chips are maintained at a temperature below about 275 C. However, the sawdust reaches a substantially higher temperature in the exothermic decomposition process. In general,' the reaction mixture is heated gradually to an internal average temperature of from about 200 C. to about 260 C. The reaction mixture is maintained at this tem perature until the distillation of furfural is completed, normally for a period of from about one and one-half to about four hours, and preferably for about two to about three hours. 1

Subsequent to the removal of the furfural from the reaction mixt'ure, the residue, which consists of brown, relatively large chips and charred sawdust, is heated-to a tempe'rature'of from about 425 C. to about 500 C.,

The preferred material is sawdust, having thermically to decompose and to heat the larger chips and to produce organic acids effective to catalyze the conversion of the pentosans present in the large chips to furfural. The large chips were maintained at a temperature below about 260 C. The decomposing sawdust reached higher temperatures on the order of about 300 C. The internal temperature of the reaction mixture at the time the exothermic decomposition of the sawdust started was about 200 C. The reaction mixture was maintained at an average internal temperature of about 200 C. to about 260 C. for period of about two to about three hours. The gases which were evolved from the reaction mixture were passed through the outlet of the still into the condenser where they were condensed. The condensate contained five pounds of furfural in addition to methyl alcohol, organic acids including acetic acid and formic acid, and acetone. The furfural was recovered from this condensate by conventional methods knownto the art.

The residual wood material in the still which consisted of brown wood chips and somewhat charred sawdust amounted to slightly over of the original dry weight of the starting material. The temperature of this wood residue was increased to about 450 C. Tar and other volatile materials escaped through the outlet of the still and approximately thirty-five pounds of high quality charcoal were obtained in the still. The charcoal was sub jected to a slight Water spray to facilitate its safe r..- moval from the still pot.

lt will be appreciated that the mixture of wood parti cles can be heated by means other than those described in the foregoing example. For instance, a mass of saw: dust may be heated to a temperature requisite to eliect exothermic decomposition thereof, and a suitable reaction tar and other volatiles are distilled out and removed, and

the wood residue is converted to charcoal.

' Example I 120 lbs. of wood chips obtained from a mixture of oak, beech and maple wood ,'and consisting of 100 lbs. of dry wood substance and 20 lbs. of water were mixed 'with 25 lbs. of sawdust obtained from the same mixture of wood and containing about 20 lbs. of dry'wood substance and about 5 lbs. of water. The chips were char-v acterized by an average thickness of about threc-eighths of an -iuch and were about one inch long and, about one? eighth of an inch wide. The sawdust consisted essentially ofparticles of between six and twenty mesh. v 1

The mixture of chips and sawdust was introduced into afst-ill provided with suitable inlets and outlets for the introduction of gases and vapors. The inlets into the still were connected to a source of hot gases from a small coal burner. The outlets from the still were connected to a condenser. Hot gases were introduced into the still from the burner at a temperature of about 350 C. and were effective to gradually raise the temperature of the mixture in a manner such that the "sawdust began exomixture of. large and small wood particles thereafter combined therewith.

It will be appreciated that bythe process of this invention, acids effective to catalyze the conversion of the pentosans in the large wood chips to furfural are obtained integrally in the process itself, thereby avoiding undue contamination of the volatilized products. Furthermore, the process results in consistently high yields of furfural in good concentration in the distillate from the reaction mixture. Additionally, the process is effective in leaving the wood residue in perfect form for conversion into high quality charcoal.

I claim: l. The process for producing furfural and charcoal which comprises forming amixture of relatively large pieces of wood and sawdust having a particle size not greater than about six mesh there being present in said mixture from about oneto about ten parts by weight on a dry basis of said sawdust for each ten parts by weight on a dry basis of said large pieces of wood, heating said mixture gradually to an elevated temperature to effect exothermic decomposition of said sawdust, without SllbStaI-l'. tial exothermic decomposition 'of the large wood pieces, to produce by exothermic decomposition of said sawdust organic acids efifective under the conditions to catalyze the conversion of the pentosan's resent in said large wood pieces to produce turfural, said large wood pieces being heated by the exothermic decomposition of said sawdust, separating the 'furfural so produced from the reaction zone, and thereafter'heating the remaining wood residue to a temperature in excess of the exothermic 'decomposi tion point thereof toproduce charcoal. j 2. The process of claim 1 wherein the sawdust has a mesh size of from about five to about twenty. 3. The process of claim 2 wherein said large wood pieces and said sawdust contain from about 10% to about 20% by weight of moisture and wherein there is present from about one to about five parts by weight on a dry basis of said s'awdust'for each ten parts by Weight of said large wood pieces.

l. The process of claim 1 wherein the temperature of the large wood pieces is maintained below about 260 C. during the furfural forming step.

5. The process of claim 1 wherein the mixture of large wood pieces and small particles of wood is gradually heated to and maintained at an average internal temperature of from about 200 C. to about 260 C. during the furfural forming step.

References Cited in the file of this patent UNITED STATES PATENTS 1,380,262 Stafford May 31, 1921 5 1,397,181 Poore Nov. 15, 1921 FOREIGN PATENTS 872,686 France Feb. 23, 1942 

1.THE PROCESS FOR PRODUCING FURFURAL AND CHARCOAL WHICH COMPRISES FORMING A MIXTURE OF RELATIVELY LARGE PIECES OF WOOD AND SAWDUST HAVING A PARTICLE SIZE NOT GREATER THAN ABOUT SIX MESH, THERE BEING PRESENT IN SAID MIXTURE FROM ABOUT ONE TO ABOUT TEN PARTS BY WEIGHT ON A DRY BASIS OF SAID SAWDUST FOR EACH TEN PARTS BY WEIGHT ON A DRY BASIS OF SAID LARGE PIECES OF WOOD, HEATING SAID MIXTURE GRADUALLY TO AN ELEVATED TEMPERATURE TO EFFECT EXOTHERMIC DECOMPOSITION OF SAID SAWDUST, WITHOUT SUBSTANTIAL EXOTHERMIC DECOMPOSITION OF THE LARGE WOOD PIECES, TO PRODUCT BY EXOTHERMIC DECOMPOSITION OF SAID SAWDUST ORGANIC ACIDS EFFECTIVE UNDER THE CONDITIONS TO CATALYZE THE CONVERSION OF THE PENTOSANS PRESENT IN SAID LARGE WOOD PIECES TO PRODUCE FURFURAL, SAID LARGE WOOD PIECES BEING HEATED BY THE EXOTHERMIC DECOMPOSITION OF SAID SAWDUST, SEPARATING THE FURFURAL SO PRODUCED FROM THE REACTION ZONE, AND THEREAFTER HEATING THE REMAINING WOOD RESIDUE TO A TEMPERATURE IN EXCESS OF THE EXOTHERMIC DECOMPOSITION POINT THEREOF TO PRODUCE CHARCOAL. 